I have two circuits in my main breaker panel.

Circuit 1 is on a 2 pole 60amp GFCI breaker. It goes directly outside from the breaker box and does not interact with the house aside from at the main breaker box.

Circuit 2 is a single pole 20amp breaker that feeds lights in the garage.

Some times (not all the time) when I flip a switch to turn on the garage lights (circuit 2), the GFCI breaker on circuit 1 trips.

I have opened all of the light cans and switch box on circuit 2 and everything seems wired correctly.

I have tested all wires on circuit 1 for shorts to ground and shorts between wires. All tested fine.

There is no possibility of the two circuits sharing a neutral on the load side.

How can this be?

  • Are the garage lights incandescent, fluorescent, or LED? – ThreePhaseEel Oct 22 '20 at 11:42
  • I'm having a very similar problem in my building and have posted in this website a few weeks back. My current troubleshooting step is to disconnect each light one at a time to see if I'm getting any EMI from one of the lights as I've heard it can cause issues with GFCI, you might try the same. – ed729 Oct 22 '20 at 13:14
  • There are fluorescent and incandescent lights on that circuit. – Dcliff9 Oct 22 '20 at 18:21
  • @Dcliff9 -- try turning the garage breaker off, disconnecting all the fluorescent lights, capping them off, turning the garage breaker on again, and seeing if you can reproduce the problem. Also, do the garage fluorescents use old heavy magnetic ballasts, or new feathery-light electronic ballasts? – ThreePhaseEel Oct 22 '20 at 23:57
  • @ThreePhaseEel - They are all screw-in fluorescents. I have taken them out for now and will let you know if that makes any difference. Can you tell me what your theory is? I’m struggling to understand how one circuit could trip a GFCI breaker on a separate circuit if they aren’t sharing a neutral. – Dcliff9 Oct 24 '20 at 5:10

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